Onboard Training (OBT) has been recognized as one of the most effective means of practical training for seafarers as part of Maritime Education and Training. The International Convention on Standards of Training, Certification and Watchkeeping for Seafarers 1978, as amended prescribes 12 months as the minimum mandatory seagoing service for candidates for officers in charge of a navigational watch. Within this period, cadets are required to complete their OBT requirements which may include Training Record Book tasks, project work, among others. In terms of cadets’ work and rest hours onboard the ship, the Maritime Labour Convention, 2006 (MLC, 2006) stands as a pivotal governing international instrument including the working and living conditions of seafarers, in general. This study aimed to determine the relationship between the amount of work and rest hours to the productivity of deck cadets in a structured OBT program onboard a training ship. Through quantitative research, the researchers gathered the records of work/rest hours of 53 deck cadets during their training program and analyzed their OBT documents to determine their progress. Results showed that the cadets were able to accomplish their OBT requirements within the allowable work hours as stipulated in MLC, 2006. Further, the researchers concluded that there is no relationship between the number of rest hours and their productivity, which was attributed to the merits of a structured OBT program. This study recommends to look for opportunities to improve the structured OBT program onboard training ships, and furthermore, investigate the same onboard commercial vessels setting.